This image of the lit face of Saturn's outer, or A ring was taken by the Cassini spacecraft shortly after crossing the ring plane after its orbit insertion burn. The image was taken with the narrow angle camera on July 1, 2004. The rings in the middle of the image are approximately 134,000 kilometers (83,200 miles) from the center of Saturn.
The bright wave pattern near the center of the image is caused by the overlap between spiral waves of varying particle density generated by Saturn's moons Janus and Epimetheus, which share an orbit. These two moon orbital periods are very close to each other and, at this location, affect ring particle orbits.
Cleaner spiral patterns caused by single satellites can be seen in other images; some of the weaker wave patterns in this image are also spiral patterns generated by smaller moons outside the main rings. All these spiral waves are of the same nature as the arms of spiral galaxies. The finest features which can be discerned (inwards, or to the left, of the bright wave feature in the center) are less than one mile across. Their cause is not currently known.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The Cassini orbiter and its two onboard cameras, were designed, developed and assembled at JPL.
For more information, about the Cassini-Huygens mission visit, http://saturn.jpl.nasa.gov.